1. Field of the Invention
The present invention relates to a developing unit and an image forming device including the developing unit.
2. Description of the Related Art
Generally, laser printers that use non-magnetic single component toner include a process cartridge for developing images. This process cartridge includes a photosensitive drum, an agitator a toner camber, a supply roller, a developing roller, and a thickness regulating blade.
The agitator is provided in the toner chamber for agitating toner housed in the toner chamber in order to apply a charge to the toner and also to discharge the toner toward the supply roller. Rotation of the supply roller supplies the discharged toner to the developing roller. The toner thickness regulating blade applies pressure to the developing roller to form a uniform thin-thickness toner layer on the developing roller. At this time, friction between the thickness regulating blade and the developing roller applies sufficient charge to the toner.
The laser printer also includes a charging unit and a laser emitting unit. The charging unit uniformly charges the surface of the photosensitive drum. The laser emitting unit scans the uniformly charged surface of the photosensitive drum with a laser beam at a high rate of speed based on image data, thereby forming an electrostatic latent image on the photosensitive drum. When the electrostatic latent image comes into confrontation with the charged toner carried on the developing roller as the photosensitive drum rotates, the toner is selectively transferred onto the photosensitive drum to develop the electrostatic latent image into a visible toner image.
A paper sheet is fed by sheet feed rollers from a paper supply cassette. While the paper sheet is transported between the photosensitive drum and a transfer roller, the toner image formed on the photosensitive drum is transferred onto the paper sheet. Then, fixing rollers fix the toner image onto the paper sheet, and discharge rollers discharge the paper sheet.
In this type of image forming device, the agitator and the developing roller are constantly driven. That is, the toner particles are constantly colliding with one another in the toner chamber because of the rotation of the agitator. Also, the toner particles are constantly scraped between the toner thickness regulating blade and the developing roller because of the rotation of the developing roller. This degrades the toner and also wears down the developing roller.
In order to overcome such problems, there has been provided a control method to control the agitator and the developing roller to start rotating when a paper sheet is supplied and to stop the rotation when a toner image is completely transferred onto the paper sheet.
However, when a prescribed time has elapsed after a previous image forming operation has been completed, the charge of the toner that was charged during the previous image forming operation gradually drops. In this case, even if the agitator and the developing roller start rotating when a paper sheet is supplied for a subsequent image forming operation, the toner will not be sufficiently charged by the time developing operations are performed. Such insufficiently charged toner gives rise to poorly developed images.
In view of the foregoing, it is an object of the present invention to overcome the above-described problems, and also to provide a developing unit and an image forming device including the developing unit capable of developing high-quality images using adequately charged toner even during an image forming operation performed a prescribed time after completion of a previous image forming operation.
In order to achieve the above and other objectives, there is provided a developing device used in an image forming device including a feeding mechanism that feeds a recording medium. The image forming device performs an image forming operation based on image data received from an external device for forming an image on the recording medium. The developing device includes a photosensitive member, a developing agent chamber, a developing unit, an agitating member, a judging unit, and a driving member. The developing agent chamber houses a developing agent. The developing unit selectively supplies the developing agent housed in the developing agent chamber to the photosensitive member. The agitating member is housed in the developing agent chamber and agitates the developing agent housed in the developing agent chamber. The judging unit judges whether or not a charging amount of the developing agent is sufficient or insufficient when the image forming operation is started. The driving member drives the agitating member and the developing unit. When the judging unit judges that the charging amount of the developing agent in insufficient, the driving member starts driving at least one of the developing unit and the agitating member before the feeding mechanism starts feeding the recording medium.
There is also provided a developing device used in an image forming device. The image forming device includes a feeding mechanism that feeds a recording medium and performs an image forming operation based on image data received from an external device for forming an image on the recording medium. The developing device includes a photosensitive member, a developing agent chamber, an agitating member, a judging unit, and a driving member. The developing agent chamber houses a developing agent. The developing unit supplies the developing agent housed in the developing agent chamber to the photosensitive member. The agitating member is housed in the developing agent chamber and agitates the developing agent housed in the developing agent chamber. The judging unit judges whether a charging amount of the developing agent is sufficient or insufficient. The driving member drives the agitating member and the developing unit. When the judging unit judges that the charging amount of the developing agent is insufficient, the driving member drives at least one of the developing unit and the agitating member for a time duration longer than when the judging unit judges that the charging amount of the developing agent is sufficient.
Further, there is also provided an image forming device for performing an image forming operation. The image forming device includes a feeding mechanism, a photosensitive member, a developing agent chamber, a developing unit an agitating member, a judging unit, and a driving member. The feeding mechanism feeds a recording medium. The developing agent chamber houses a developing agent. The developing unit selectively supplies the developing agent housed in the developing agent chamber to the photosensitive member. The agitating member is housed in the developing agent chamber and agitates the developing agent housed in the developing agent chamber. The judging unit judges whether or not a charging amount of the developing agent is sufficient or insufficient when the image forming operation is started. The driving member drives the agitating member and the developing unit. When the judging unit judges that the charging amount of the developing agent is insufficient, the driving member starts driving at least one of the developing unit and the agitating member before the feeding mechanism starts feeding the recording medium.